The current production of high-degree and commercially-valuable copper and zinc concentrates is having technical difficulties, since during the ore deposit exploitation, low-grade areas of metals having a commercial value have been found, and which due to the mineral complexity in the deposit, makes non-profitable the flotation-based obtainment of the concentrate in beneficiation plants. The presence of arsenic and antimony impurities makes the commercial concentrate (copper, zinc) to have an economic penalization, thereby reducing its commercial value.
The obtainment of copper has traditionally been carried out from the casting of ore concentrates in furnaces, in order to produce a “Blister” copper having 98.5% purity, which is subsequently poured to anodes and, finally, it is electro-refined in order to obtain a high purity cathodic copper (99.999%).
Also, the extraction of copper is made by hydrometallurgical processes, such as the leaching in lumps or beds of low-grade ore having secondary oxides or sulfides non-susceptible to flotation, and the purification by solvent extraction, which is currently preferred due to its low-cost and less adverse environmental effects.
The current obtainment process for zinc has traditionally been carried out by a roasting system of zinc concentrates in a fluidized-bed furnace in order to oxidize the ore, thus generating a calcine, which is subsequently treated by a hydrometallurgical process, wherein the zinc is recovered in a solution being refined and purified, in a final step, the metal in solution is electro-deposited in aluminium cathodes, the zinc is obtained as metal sheets, and casted for its shaping in zinc bars with a high degree of purity (SGH). This process has drawbacks to process concentrates having impurities such as iron, arsenic, antimony, among others.
The use of thio-oxidizing and/or iron-oxidizing microorganisms in the ore and copper or zinc sulphide-based concentrates dissolution process, is known as bioleaching and has been used as an alternative to the extraction of base metals. Ores and/or sulphide-based concentrates of copper, zinc, nickel, cobalt, have been treated in processes such as heapleaching or continuous leaching in stirred tanks.
One of the processes for the treatment of copper and zinc sulphide-based concentrates uses continuous-flow stirred-tank type reactors having aeration systems, which are placed in series, wherein the concentrate or ore (metal sulphide) finely milled is added to the first reactor together with inorganic nutrients. The ore pulp flows through the reactors at controlled pH and temperature, and it contains microorganisms that carry out the dissolution of the mineral species present in the concentrate; in this case, it is performed by using iron-oxidizing and thio-oxidizing acidophilic microorganisms, which live at temperatures in the range of 25° C. to 90° C., and which are able to tolerate high acidic levels and dissolved metallic ions.
One of the biggest challenges during the operation of the stirred tanks is the coexistence between the amount of solids (pulp density) maintained in suspension and the presence of microorganisms. The processes currently developed are limited to no more than 15% in pulp density since issues occur as a result of physical damage to the microorganisms, thereby inhibiting the dissolution.
Since the microorganisms used are temperature dependent for their growth, processes by operating type and temperature have been developed. Microorganisms that have been widely used in bioleaching processes are mesophilic bacteria as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptosprilium ferrooxidans at temperatures near to 40° C. Thermophilic bacteria of the type Sulfolobus, and archaea as Sulfolobus spp have been used due to their potential to increase the extraction kinetics of metals from sulphide ores at temperatures above 50° C. The minerals depleted from this bioleaching step are removed and sent to confinement. During the bioleaching step, copper and zinc are obtained in a ionic form in a sulphate media.
Once obtained the solution rich in copper and/or zinc, it is necessary to perform the separation, concentration, purification and recovery of these metals in solution, thereby involving the use of water-immiscible organic extractants, dissolved in organic solvents (organic phase). The aqueous solution with the obtained metals is contacted with specific extractants such as Aldoximes, Ketoximes and phosphinic acids, and through the chemical reaction of interchange or transfer between the proton and the metal cation, it allows separating the cation of economic interest, which is transferred to the organic phase. In order to concentrate the metal ion of interest and to regenerate the organic phase for its reuse, an acid environment is used, producing a concentrated metal solution that is sent to electrolysis in order to obtain the refined metal.
Among the patents having been developed for the treatment of copper or zinc metal sulphide-based concentrates there is, for example, Patent Application WO00/23629 A1, wherein a method for biolixiviating copper concentrates is shown, wherein a copper ore is subjected to a process involving iron/sulfur oxidizing microorganisms in order to obtain a copper-containing solution, said solution is contacted with a mixture of a commercial extractant and organic solvent to partially extract the copper from the solution. When contacting the organic phase in the solvent extraction step the copper is concentrated. Once a concentrated and purified solution has been obtained, it is processed in an electrolysis step.
According to Patent Application WO01/18266 A1, a method for zinc recovery is shown, by means of an integrated bioleaching and solvent extraction system, which is proposed as an alternative for the treatment of zinc. Mainly, metallic zinc and byproducts such as copper and plaster are obtained, which can be marketed and/or confined according to the current environmental legislation.
In Patent WO9428184 A1, zinc recovery is proposed by means of a combined process of zinc concentrates bioleaching and solvent extraction, wherein Diethyl-hexyl phosphoric acid (D2EHPA) is used as organic extractant, and lonquest 801 as a diluent to specifically recover zinc from sulphate solutions.
As may be seen, in the current state of the art, the use of combined processes of bioleaching and solvent extraction for the selective recovery of copper or zinc is described; however, the processes described in the prior art, have the disadvantage of being unable to be used with pulp densities higher than 15%, having high contents of arsenic and iron, and further they consume an excessive amount of oxygen during the bioleaching process.
Therefore, it has been sought to overcome the drawbacks of the prior art by means of the development of a bioleaching and solvent extraction process with selective recovery of copper and zinc from sulphide polymetallic concentrates, which allows the handling of pulp densities higher than 15%, with high contents of iron and arsenic, and having a more efficient operation through less oxygen consumption during the bioleaching.